a ojo

My attempt:The charts were constructed by courses of compass and distances considered by“ the eye of a good sailor”.
or The charts were constructed by courses of compass and distances considered by“ the rule of thumb”
I don't like them at all, so would you be son kind and help me. Thank you.

Re: a ojo

Since we are talking about compasses, maps and charts, what about the following sentence?las otras cuatro presentan la misma estructura: el centro de cada circunferencia directriz de dieciséis nudos de vientos de 282 milímetrosde diámetro

My attempt:the other four display the same structure: the center of each directive circumference of sixteen wind knots of 282 millimeters of diameter